polyurethane foams are typically produced from a polyol and a polyisocyanate. Polyurethane foams are well known in the art and have numerous applications. Rigid and semi-rigid foams are used in a wide variety of applications, in turn requiring an extensive range of foam properties. A significant number of different polyol grades are required to be able to manufacture the different foams. Yet, it remains difficult to meet all the desired properties and compromises may have to be made.
A variety of polyols have been proposed for use in the manufacture of polyurethane foams, including polyether polyols such as those marketed under the tradename CARADOL and TERATHANE and POLYTHF and polyester polyols such as those marketed under the tradename TONE and FORMREZ.
International PCT publication No. WO 97/00902 discloses the preparation of polyurethane foams, in particular resilient, flexible foams, from an aromatic polyisocyanate having a functionality of from 2.5 to 3.0 isocyanate groups per molecule and a polydiene diol having a number average molecular weight from 1,000 to 20,000 and a functionality of from 1.6 to 2 hydroxyl groups per molecule.
It is known to use mixtures of polyols to prepare polyurethane foams having desired properties. Examples of polyol mixtures for use in the preparation of rigid and semi-rigid polyurethane foams include those marketed under the tradenames CARADOL PP520-03, LP585-01, LP530-03, GB450-01, GB475-01, GB250 and the like.
U.S. Pat. No. 4,752,626 describes the preparation of a high resilience urethane foam. The foaming system is composed of a thixotropic polyisocyanate component and a thixotropic polyol component. The polyol component comprises a polyol blend of a polyolefinic polyol and a polyoxyalkylene polyol in a weight ratio between 95/5 to 50/50.
It will be appreciated that there is still room for improvement in this field. In particular, there is a need for improving adhesion of rigid and semi-rigid polyurethane foams to polyolefins, including copolymers of olefin monomers, and block copolymers comprising more than 50% by weight of at least one polyolefin block, without, however, a significant impact on other desirable properties of the foam.
Thus far, it has been difficult to adhere polyurethane foams strongly to polyolefins without the use of a separate adhesive layer. In particular, polyurethane foams are known not to adhere strongly to thermoplastic polyolefins without the use of a separate adhesive layer.
Surprisingly, rigid and semi-rigid polyurethane foams have now been found having one or more advantageous properties as compared to prior art foams of this type. In particular, foams have been found which are capable of adhering very strongly to polyolefins and block copolymers comprising more than 50% by weight of at least one polyolefin block, by using a specific polyol mixture.